A comparative study of motor coordination underlying vocal production is proposed. Emphasis is placed on the elucidation of interactions among particular neuro-motor systems identified as integral components of the vocal system. Sound production in songbirds, an established model for certain problems in human speech, is used as the experimental paradigm. Songbird phonation is known to entail both lateralization as well as coordinated interaction of the two sides of the functionally two-parted syrinx. Recent work also implicates a vocal tract filter in production, and suggests that the properties of this filter are actively coordinated with syringeal output. A parametric comparison will be made of vocal deficits resulting from three techniques for disabling one syringeal side (1) denervation, 2) obstruction of airflow, and 3) immobilization of the vibration source) in three species chosen to represent a range of predicted interaction or independence of the two syringeal sides. This study will clarify the interpretation of peripheral contributions to functional lateralization of vocal control, presently clouded by the different results obtained in previous studies. A technique will be developed to non- permanently disable one syringeal side. These techniques will subsequently be applied to two additional bird species for which preliminary data suggest that the presence or absence of bilateral syringeal interaction is a learned motor skill. Morphological techniques will be used to characterize the static filter properties of the vocal tract. Implanted probe-tube speakers and microphones, and further analysis of vocal output in an altered- density atmosphere, will assess active filter properties in vivo. The motor components involved in controlling the vocal filter will be identified, in part, using video analysis of the motions of vocalizing birds. This identification will be verified, and the mechanisms of coordination of the filter assessed, using denervation of target motor systems. New techniques will be applied for automated computer analysis of recorded sounds. Coordination of diverse motor systems in producing organized behavior is the focus of much neurobiological research on peripheral and central contributions to neuromuscular control. The analysis of birdsong has proven particularly useful in understanding related problems in human speech. These results will have implications for understanding the relationships among neural lateralization, motor development, and learning in vocal production.